Present day telecommunications technology utilizes, to an increasing extent, optical fibers for signal transmission. The use of optical fibers, in turn, requires numerous collateral components especially adapted to handle the light or optical transmission, among which are optical fiber connectors, which are essential to virtually all optical fiber systems. Connectors may be used to join segments of fibers together to create longer lengths; to connect a fiber or fibers to active devices forming part of the communication system such as radiation sources, detectors, amplifiers, repeaters, or the like; or to connect the fibers to various types of passive devices such as switches, dividers, or attenuators. It is highly desirable, if not necessary, that the connectors perform their function with a minimum of signal loss, and that the making of a connection be a simple and as quickly accomplished as possible. The central function of an optical fiber connector or connectors, which most often are in butting relationship, is the positioning and maintenance of two optical fiber ends so that their central cores are aligned and in contact with each other, thus insuring maximum transfer of optical signals from one fiber to the other. Achieving this desideratum is a particularly challenging task inasmuch as the light carrying region (the core) of an optical fiber is quite small, being on the order of eight microns (8 .mu.m) diameter for single mode glass fiber. Another function of an optical fiber connector is to provide mechanical stability and protection of the actual connection in the working environment. Achieving maximum signal transfer (minimum insertion loss) is a function of the alignment of the fiber cores, the width of the gap between the fiber ends, and the surface condition of the fiber end faces. Stability and junction protection are generally functions of the connector design including the material used. For example, a connector generally includes a glass or ceramic cylinder which contains the fiber to be connected, and the end face of which is designed to butt against the end face of a similar cylinder in the mating connector. Such a cylinder is commonly called a ferrule, and it not only functions to align the core of the fiber, but, also, its end face is sufficiently smooth and flat to insure a uniform butting against the end face of the mating ferrule.
There are, at present, many different types of connectors in use, all of which are aimed at achieving low insertion loss within the connection, and stability. One such connector is shown in U.S. Pat. No. 4,934,785 of Mathis et al., and comprises a cylindrical ferrule, a base member which holds the ferrule, a compression spring, and a housing surrounding the ferrule and the spring. The ferrule is held rigidly in the housing by suitable adhesive, and the compression spring applies an axial force to the ferrule and housing sot hat the end face of the ferrule is maintained in contact with the mating ferrule of the second connector. Although such a connector performs its functions well, it has a high parts count assembled in a relatively complex arrangement. A high parts count means a more expensive connector, and, further, the risk of lost parts during assembly, especially in the field. With the increasing use of optical fibers as the transmission media of choice, there is a need for high density interconnect arrangements, hence, expensive connectors with a high parts count unduly increase the cost of such interconnection arrangements.
Another type of connector is shown in U.S. Pat. No. 5,481,634 of Anderson et al. and comprises a cylindrical ceramic ferrule contained in a plastic base member to form the fiber holding structure. The fiber holding structure is mounted within a cylindrical housing having an opening therein through which the ferrule protrudes. A cylindrical spring surrounds the base member and interacts with an interior surface of the housing to urge the ferrule axially outward from the housing opening. The housing has a cantilever type spring latch located on one exterior side of the connector which is manually operable and which mates with a shoulder within the receptacle to lock the connector therein. While this particular type of connector lends itself readily to miniaturization, it has a fairly high part count and is, therefore, subject to the same objections as the Mathis et al. connector. Additionally, the compression spring is, in essence, a loose part, and therefore can easily be misplaced or lost during assembly of the connector.
Both of the aforementioned connectors are representative of prior art types, virtually all of which use coil springs to apply the contacting force. In many connectors, the springs also compensate for over-travel. That is, when a connection is made with an LC type connector (Anderson et al.), the ferrule first seats on the optical interface of the mating ferrule (or active device). It is then necessary for the plug housing to continue to advance until the cantilever latch clears the latching shoulder on the receptacle or adapter. The spring absorbs this additional axial advance and once the latch is engaged, the spring, being compressed, continues to apply an axial force between the latch and the plug body to maintain intimate contact at the interface.
Glass optical fibers have, heretofore, been primarily used to bring optical signals to subscriber premises, where they are transformed into electrical signals for distribution throughout the premises. However, there has been a move toward extending the optical signals into and throughout the subscriber premises due to the development of plastic optical fiber (POF). POF has many advantages over glass optical fiber (GOF) for such use. POF is not as brittle as GOF, and does not require extremes of care in handling. POF is less expensive than GOF, thus making it attractive for local usage. Also, POF does not normally require the precision of alignment required by GOF. On the other hand, POF has higher signal loss, not having the optical transmissivity of GOF, and hence is preferably used only in short transmission spans, such as within the subscriber premises. It is anticipated that various connections to the several types of apparatus are to be made by the subscriber or customer, hence, the connections will be facilitated by less complicated or sophisticated connectors. Such connections may be made to VCR's, television sets, camcorders, and other types of domestic equipment as well as to telephones, computers, and the like.
In U.S. patent application Ser. No. 09/019,240 of Carlisle et al., now U.S. Pat. No. 6,017,154, there is disclosed a connector for terminating an optical fiber cable, that is especially designed for use with plastic optical fiber. The connector comprises a plug having a bore extending therethrough which, in turn, has an enlarged diameter threaded portion extending from within the plug to the cable entrance end. The diameter of the threaded portion is such that the threads grip the soft resilient jacket of the POF cable. Inasmuch as the jacket is bonded to the fiber (in POF), when the jacket is screwed into the plug, the POF is firmly held therewithin. Such an arrangement works quite well, however, it requires the molding or cutting of threads within the plug.
What is needed, and what the prior art appears to be lacking, is an optical connector having a low part count, reduced size, and which is readily insertable and removable from an associated receptacle without a tool or the need to grasp the opposite sides thereof which is difficult to do when a number of connections are crowded together, while insuring that positive optical contact is made with the mating connector or equipment terminal and, further, is readily and quickly applied to, for example, a plastic optical fiber or cable.